class groundTrackObject extends trackobject {
  constructor(modal, objData) {
    super(modal, objData);
  }
  update(tick) {
    super.update(tick);
    // 加上和地面的同步移动
//    if(!parent) {
      this.x += backgroundobject.inst.x_vel;
      this.y += backgroundobject.inst.y_vel;
//    }
  }
}